Diatomaceous earth is composed of the remains of ancient diatoms, microscopic one-celled plants that fill the oceans and are also found in fresh water. As the ancient diatoms died, their tiny, hard shells eventually settled to create the sludgy floor of the oceans. Diatom remains were left behind in dried ancient sea-beds which are found all over the world. The fossilized shell remains are called diatomaceous earth, which is mined for use in manufacturing and as an organic pesticide.
Living diatoms are microscopic single-celled algae. The one-cell body is surrounded by a beautiful "shell" in intricate formations made of silica.The shells are actually in two sections that open and close, similar to the action of a clam shell. Silica is not a chemical, it is a mineral, and is a completely inert substance. Diatomaceous earth is organic and completely safe.
Diatomaceous earth is mined as a sedimentary rock. It is milled into powder and graded, with the highest medical or food grade being a pure white, extremely fine powder. Lesser grades become slightly gray, and they are used for various applications.
Swimming pool filters contain diatomaceous earth. This kind has been chemically treated, and is not the same as other grades. It should only be used in swimming pool filters, and never on the garden or as an insecticide.
The tiny shells are porous, filled with miniscule cavities something like a sponge. Due to this basic structure, regular diatomaceous earth can filter extremely tiny, microscopic particles from liquids, including e.coli bacteria and viruses. It is used in filters for drinking water, beer, and syrups.
The razor-sharp silica shells are deadly to insects. A simple dusting of diatomaceous earth powder wherever insects exist will kill them. It slices tiny cracks in their exoskeletons, and they dehydrate and die. There is absolutely no danger to humans, pets or livestock. It can be dusted directly on food crops immediately before harvest. It is, however, a non-selective killer, and it will harm beneficial insects as well as harmful ones.
How to Use in the Garden
Apply diatomaceous earth with any regular garden duster. Use it after rainfall or watering so it won't be washed away; you want the powder to stay on the leaves as long as possible so the insect pests will move across it. Dust it directly on bugs that you see. It does not have a quick knock-down effect as chemical neurotoxins do, but even Japanese Beetles will be dead in about 2 days.
Don't use diatomaceous earth as a preventative insecticide. Only use it when you have an infestation. It will indiscriminately kill bees, lady bugs, and biological control insects that you want to keep in your garden.
Wear a filter mask and eye protection when you work with diatomaceous earth. While it is not toxic, and is even taken internally for various health reasons, you should not breathe the dust or get it in your eyes because its powerful drying properties can be an irritant.